1. Field of the Invention
The present invention relates to an ink-jet printhead. More particularly, the present invention relates to a bubble-jet type ink-jet printhead, a manufacturing method thereof, and a method of ejecting ink.
2. Description of the Related Art
Ink ejection mechanisms of an ink-jet printer are largely categorized into two types: an electro-thermal transducer type (bubble-jet type) in which a heat source is employed to form a bubble in ink causing ink droplets to be ejected, and an electro-mechanical transducer type in which a piezoelectric crystal bends to change the volume of ink causing ink droplets to be expelled.
With reference to FIGS. 1A and 1B, a conventional bubble-jet type ink ejection mechanism will now be described. When a current pulse is applied to a heater 12 consisting of resistive heating elements formed in an ink channel 10 where a nozzle 11 is located, heat generated by the heater 12 boils ink 14 to form a bubble 15 within the ink channel 10, which causes an ink droplet 14xe2x80x2 to be ejected.
To be useful, an ink-jet printhead having this bubble-jet type ink ejector must meet the following conditions. First, it must have a simplified manufacturing process, i.e., a low manufacturing cost and a high volume of production must be possible. Second, to produce high quality color images, creation of minute satellite droplets that trail ejected main droplets must be prevented. Third, when ink is ejected from one nozzle, or ink refills an ink chamber after ink ejection, cross-talk with an adjacent nozzle, from which no ink is ejected, must be prevented. To this end, a back flow of ink in the opposite direction of a nozzle must be avoided during ink ejection. Another heater 13 illustrated in FIGS. 1A and 1B is provided for this purpose. This second heater 13 is similarly capable of forming a bubble 16. Fourth, for high speed printing, a cycle beginning with ink ejection and ending with ink refill must be as short as possible. That is, an operating frequency must be high.
However, the above conditions tend to conflict with one another, and furthermore, the performance of an ink-jet printhead is closely associated with structures of an ink chamber, an ink channel, and a heater, the type of formation and expansion of bubbles, and the relative size of each component.
In efforts to overcome problems related to the above requirements, ink-jet printheads having a variety of structures have been proposed in, for example, U.S. Pat. Nos. 4,339,762; 4,882,595; 5,760,804; 4,847,630; and 5,850,241; European Patent No. 317,171, and an article by Fan-Gang Tseng, Chang-Jin Kim, and Chih-Ming Ho entitled, xe2x80x9cA Novel Microinjector with Virtual Chamber Neckxe2x80x9d, IEEE MEMS ""98, pp. 57-62]. However, the ink-jet printheads proposed in the above patents or literature may satisfy some of the aforementioned requirements but do not completely provide an improved ink-jet printing approach.
It is a feature of an embodiment of the present invention to provide a bubble-jet type ink-jet printhead having a structure that satisfies the above-mentioned requirements.
It is another feature of an embodiment of the present invention to provide a method of manufacturing the bubble-jet type ink-jet printhead having a structure that satisfies the above-mentioned requirements.
It is a further feature of an embodiment of the present invention to provide a method of ejecting ink in a bubble-jet type ink printhead.
In order to provide the first feature, an embodiment of the present invention provides an ink-jet printhead including a substrate having an ink supply manifold, an ink chamber, and an ink channel, a nozzle plate having a nozzle, and a heater consisting of resistive heating elements, and an electrode for applying current to the heater. The ink chamber, in which ink to be ejected is filled, is formed in a substantially hemispherical shape on a surface of the substrate, a manifold is formed from its bottom side toward the ink chamber, and the ink channel linking the manifold and the ink chamber is formed at the bottom of the ink chamber. The ink chamber, the manifold, and the ink channel are integrally formed on the substrate. Thus, the substrate has a structure in which the ink chamber, the ink channel, and the manifold are arranged vertically from its surface.
The nozzle plate is stacked on the substrate, and the nozzle plate has a nozzle at a location corresponding to a central portion of the ink chamber. The heater is formed in an annular shape on the nozzle plate and centered around the nozzle of the nozzle plate. Preferably, the diameter of the ink channel is equal to or less than that of the nozzle.
In a preferred embodiment, a bubble guide and a droplet guide, both of which extend down the edges of the nozzle in the depth direction of the ink chamber are formed to guide the direction in which a bubble grows and the shape of the bubble, and the ejection direction of an ink droplet during ink ejection, respectively. The heater is formed in the shape of the character xe2x80x9cOxe2x80x9d or xe2x80x9cCxe2x80x9d so that the bubble has a substantially doughnut shape.
In order to provide the second feature, an embodiment of the present invention provides a method of manufacturing a bubble-jet type ink-jet printhead, in which a substrate is etched to integrally form an ink chamber, an ink channel, and ink supply manifold thereon. More specifically, a nozzle plate is formed on a surface of the substrate, and an annular heater is formed on the nozzle plate. The ink supply manifold is formed from a bottom side of the substrate toward the surface. An electrode for applying current to the annular heater is formed. A nozzle plate is etched to form a nozzle having a diameter less than an inner diameter of the annular heater. The substrate exposed by the nozzle is etched to form the ink chamber having a substantially hemispherical shape and a diameter greater than the annular heater. The bottom of the ink chamber is etched to form the ink channel linking the ink chamber and the manifold.
In a preferred embodiment, the ink chamber is formed by anisotropically etching the substrate exposed by the nozzle to a predetermined depth, or by first anisotropically etching the substrate exposed by the nozzle and then isotropically etching it so that the ink chamber has a hemispherical shape.
In a preferred embodiment, the ink chamber is formed by anodizing a portion of the substrate, in which the ink chamber is to be formed, to form a porous layer in a substantially hemispherical shape and then selectively etching and removing the porous layer.
In a preferred embodiment, the ink channel is formed by forming an etch mask, which exposes the substrate with a diameter less than the nozzle formed on the nozzle plate, forming the ink chamber and the ink channel using the etch mask, and removing the etch mask.
In a preferred embodiment, the ink chamber is formed by anisotropically etching the substrate exposed by the nozzle to a predetermined depth and forming a hole, depositing a predetermined material layer over the anisotropically etched substrate to a predetermined thickness, anisotropically etching the material layer to expose the bottom of the hole while forming a spacer of the material layer along a sidewall of the hole, and isotropically etching the substrate exposed to the bottom of the hole.
According to an embodiment of the present invention, a bubble is formed in a substantially doughnut shape conforming to the shape of the heater, thereby satisfying the above requirements for ink ejection. Furthermore, this embodiment permits a simple manufacturing process and high volume production of printheads in chips.
These and other features and advantages of the embodiments of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.